5 Answers
5

A short shutter-speed is needed to freeze an object in motion. The faster the object, the shorter the shutter-speed you need. It also depends if the motion is close or far and its direction, so we cannot tell you exactly how fast a shutter-speed is needed.

When buying a camera, you can look for the maximum shutter-speed of the camera. That lets you know how fast it can exposure. Usually, 1/2000s is very common and would freeze pretty much any person but if you are trying to freeze a racing car for example, it wont do. A few recent cameras go to 1/16,000s. Those are the Nikon 1 series of mirrorless cameras. Casio makes some fixed-lens that reach 1/40,000s.

There are object such as bullets which are way too fast for most cameras to capture and for that a fast shutter-speed is simulated by using a very short burst of flash. For that you need a camera with dedicated flash unit and controlled environment, so that the flash produces most of the illumination. Search of high-speed photography if that interests you.

As per the comments below, @dpollitt has a point. The object you are shooting must be in focus and autofocus can along focus so fast. Some cameras are better than others but there is a point when no autofocus can keep up with a speedy object. My advice is to use manual focus for objects which have a predictable path and set your focus to the place when the object will be when you take your shot.

Good answer, but I think autofocus is an important part of this discussion. If you miss focus due to poor performing AF, your shutter speed won't help much! Also, see photo.stackexchange.com/a/34280/4892
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dpollittApr 26 '13 at 14:02

high shutter speed only helps if you have fast lenses that let you take a proper exposure with those high speeds, so you need to worry about the quality of the glass and the maximum aperture. ISO comes into this, too, so you need to figure out how far you can crank up ISO before noise becomes a problem (or perhaps, 'fixable' noise). With objects in motion, you end up shooting in burst mode, too, so how fast and how many images you can shoot in a burst starts to matter, and.... and it so seemed like an easy question...
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chuquiApr 26 '13 at 17:14

And I was just trying to write about shutter-speed needed to freeze motion... Maybe I should a book instead ;)
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ItaiApr 26 '13 at 23:55

Provided that the subject is in focus, two things can cause (motion) blur:

Shake/vibration of the camera

Holding your camera with a solid, steady pose will reduce the vibration. Choosing a high shutter speed will also reduce or even eliminate the blur caused by such vibrations.

Movement of the subject

A high shutter speed is required for crisp photo of a moving object. The faster it moves, the faster the shutter speed has to be.

In both case, you want to increase the shutter speed to a point where no blur is visible. You can do it with simple trial and error. The following is a rough idea of how fast your shutter has to be for certain subjects:

1/100 to 1/250 is good for shooting a walking person.

1/500 to 1/1000 for running subjects like kids or pets

1/500 is good enough for most moving cars, if the car is going really fast the wheel may still be blurry.

1/1000 is a safe minimum for most sports. For tennis, badminton and table tennis, this may still not be enough. Especially for badminton since the shuttle can travel over 300 kmph and it is actually the fastest racket-sports.

1/2000 to 1/4000 for birds in flight, if you want their wings to be sharp.

Most modern cameras can shoot at these shutter speeds. The most significant difference is noise performance when using high ISO. So if you are planning to shoot a lot of fast moving objects, ISO performance will have a direct and huge impact on the image quality that you get.

Last but not least, remember that blur is not always bad. Blur can be a great artistic way to express the motions of objects. Car advertisements for example often use blur to convey the sense of speed in a still photograph.

(Extreme cases like hummingbirds, flapping wings of insects, bullets, explosions etc are not covered here as they easily require shutter speeds so high that only cameras specially built for such purpose can provide.)

@stefun: A higher ISO will allow you to use a higher shutter speed, which will in turn freeze motion more. But, that will mean more amplification of the signal, because less light will be admitted, so the high ISO image may be worse overall. It's hard to give a general answer.
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mattdmApr 26 '13 at 15:21

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@stefun A key point you may be missing when comparing the cameras you're looking at: the numbers for ISO, shutter speed, etc., in specifications are generally limits. The camera which can do ISO 12800 can also do ISO 3200.
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mattdmApr 26 '13 at 15:23

The biggest thing is going to be shutter speed hands down. Without a fast shutter, it is going to be impossible to stop the motion in the scene. That said, there is still other factors that will help make a good quality photo at high shutter speed. A good autofocus that can follow a moving subject is critical unless the movement is going to be along the focal plane (the same distance from the lens).

Also, since a fast shutter lets in less light, the ability to shoot with a "faster" (more open, smaller number) aperture will be helpful to increase the light reaching the sensor. This will make the depth of field smaller though which will increase the need for a good autofocus. Good high ISO performance is another option that will allow for a faster shutter speed without having to open the aperture as far.

Finally, when shooting fast moving subjects, there is a good chance you will be at a distance and shooting freehand. In these cases, camera shake can have a significant impact on image sharpness. Good optical image stabilization can help reduce camera shake, but it should be noted that it can also cause lag when trying to follow a moving object if it doesn't support limiting which axises are stabilized.

As others have mentioned, to prevent blur, you want a fast shutter speed. However, when looking for a camera, this is not actually a big issue - even my ultra-low end Sony a390 supports shutter-speeds of 1/4000, which is more than fast enough for most common moving objects (I'm assuming that you're not taking pictures of bullets mid-air)

The real issue will be light; at such high shutter-speeds, not much light reaches the sensor, so what you really need to look at is the qualities that will allow fast exposures.

Here's what you should look for in a camera/lens for photographing moving subjects:

Full-frame sensor. Cameras with larger sensors will receive more light, and thus can properly expose faster.

Higher ISOs. Higher ISOs allow you to shoot in the same light level with faster shutter-speeds, at the expense of increased noise. Make sure you look at the 'normal ISO,' rather than the expanded ISO.